INTERFACIAL FATIGUE LIMIT AS MEASURE OF CYCLIC BONDING STRENGTH OF HARD COATINGS

Abstract

An interfacial fatigue test technique has been developed to evaluate the contact fatigue behaviour of various coating-substrate systems. It is shown that failure of the coated systems is initiated at the interface and that the intelfacial fatigue limit is a sensitive measure of the bonding condition between the coating and substrate which remains insensitive to the hardness of both materials and the testing conditions. This characteristic of the test is significant in that it allows the separation of bonding strength from other properties of the coating-substrate system. The nature of the test is investigated theoretically in terms of contact mechanics of both homogeneous and layered materials. It is revealed that the shear stress range at the interface is an appropriate parameter for comparing experimental results. Using the critical shear stress range at the interface for coating debonding, the cyclic bonding strengths of various coating-substrate systems can be quantitatively evaluated and compared.